Generally, an eccentric rotation-type vibration generator has been widely used as a linear vibration generating device used as a receiver in a portable terminal. However, this technology does not guarantee a long life, gives a late response, and has limitations in implementing various vibration modes. Thus, this technology does not meet the demand of consumers in the current situation where touch-type smartphones are rapidly popularized.
As a countermeasure against to the above, a linear vibration generating device for generating vibration by linearly oscillating a weight has been developed. The developed linear vibration generating device uses interactions between an electric field generated by a coil and a magnetic field of a permanent magnet surrounding the coil to linearly oscillate the weight so that a desired vibration may be generated.
Korean Patent Registration No. 1180486 (hereinafter, referred to as ‘Patent Literature’) discloses a technique of generating vibration by linearly oscillating a weight in the title of “a linear vibration motor”. The technology proposed in the patent literature has an advantage that the device may be designed in a small size while maintaining stable operation characteristics by increasing magnetic efficiency.
The linear vibrator disclosed in the patent literature will be described in more detail with reference to FIG. 1.
Referring to FIG. 1, the linear vibrator briefly includes a vibrator 115, a stator 110, and a case 135 for protecting them. The vibrator 115 includes a magnet 111 for forming a magnetic field and a weight 112 surrounding the magnet 111. The stator 110 includes a yoke 107 provided at the center of a bracket 102 and a coil 106 disposed around the yoke 107.
A PCB 105 electrically contacting the coil and transmitting an electric signal provided from the outside to the coil is disposed on a central upper surface of the bracket 102. An elastic member 120 is interposed between the bracket 102 and the weight 112 to elastically support the vibrator 115 and limit its amplitude so as to ensure smooth vibration.
This linear vibrator generates vibrations with up and down oscillations of the vibrator 115 due to the electromagnetic interaction between the stator 110 and the vibrator 115. However, during the vibration generating process, the vibrator 115 is accompanied with lateral shaking, namely tilting (see the broken lines) as well as normal up and down oscillations. There are many causes of this tilting, but the tilting is caused mainly due to the characteristics of the elastic member 120.
The tilting occurs more greatly when the vibrator 115 deviates from an overlap zone with the yoke 107 while the vibrator is in the upward stroke. In the zone where the vibrator 115 overlaps with the yoke 105, even though the tilting occurs, the inner circumference of the magnet 111 comes into contact with the outer surface of the yoke 107 to suppress serious tilting. However, beyond the zone, there is no restriction on the tilting of the vibrator 115.
A large amount of tilting that occurs beyond the zone where the vibrator 115 overlaps with the yoke 107 (the space above the yoke) causes physical contact between the case 135 and the vibrator 115 to generate noise. More specifically, an outer edge of the upper surface of the weight 112 opposite the elastic member 120 directly contacts an inner flat surface of the case 135, thereby generating noise and impact.
Tilting may not only cause noise and impact due to the contact with the case 135 but may also cause deformation of the elastic member 120, which leads to vibration frequency deformation. In other words, the tilting may cause deformation or breakage of the elastic member by concentrating the vibration force only on one side of the elastic member, which may adversely affect quality and reliability and thus result in deterioration of the durability of a product and shortening of the life span.